1. Field of the Invention
The present invention relates to a method of blindly estimating a wide band code division multiple access (WCDMA) orthogonal variable spreading factor (OVSF) code for a signal analyzer, and more particularly, to a method of blindly estimating a WCDMA OVSF code for a signal analyzer, which is capable of exactly and rapidly detecting an OVSF code at a small amount of calculation by using a zero crossing rate (ZCR).
2. Description of the Related Art
As well known in the art, WCDMA that is one of third-generation (3G) wireless communication systems described in 3GPP TS.25 is an asynchronous communication system having a chip rate of Fc=3.84 Mcps.
Conventionally, a base station and a terminal share connection information including, for example, a primary scramble code (PSC), a spreading factor (SF), a transport format combination indicator (TFCI), etc., such that the base station and the terminal may perform high-speed data communication based on the corresponding connection information during a process of decoding a physical layer signal.
To the contrary, since a signal analyzer for analyzing a reverse WCDMA signal tests a device under test (DUT) to detect a defect in a state that user equipment is abnormally operated, so that other mal-functional elements are added when the connection information described above is obtained from a user or extracted from an upper layer signal, the signal analyzer for analyzing a reverse WCDMA signal is unsuitable. Thus, it is very important that a signal analyzer for signal analysis is operated to exactly estimate the lowest level of information from a signal without any connecting operations.
In a WCDMA system, a receiver detects a reverse WCDMA signal by performing cell search and physical layer synchronization through following three steps.
First step: Slot synchronization is obtained by synchronizing sample/chip boundary through a primary synchronization channel (PSCH).
Second step: Frame synchronization and a scrambling code group are obtained through a secondary Synchronization Channel (SSCH).
Third step: fractional sample/chip boundary synchronization, scrambling code index synchronization and channel estimation are performed through a common pilot channel (CPICH).
Specifically, since a spreading code is applied to the reverse CPICH signal in the third step, it is known which a signal is used, so that it is very easy to detect it. When the CPICH can be decoded, it is possible to estimate a channel and it is possible to exactly detect a remaining DPxCH signal such as a dedicated physical data channel (DPDCH) signal or a dedicated physical control channel (DPCCH). By using the detected CPICH signal, the frequency offset, timing offset, phase offset and channel of an original signal are estimated to be compensated.
Meanwhile, in the WCDMA system, the spreading of each channel includes a channelization operation and a following scrambling operation. In the channelization operation, each data symbol is converted into a plurality of chips by being multiplied by a channelization code which is a binary sequence of ‘1’ and ‘0’, where the number of chips per data symbol is called a spreading factor (SF). The channelization code is an orthogonal variable spreading factor having a spreading factor from at least 4 to at most 512 (in a case of a down link). As a result, while the scrambling codes are used to distinguish base stations or cells from one another, the channelization codes are used to distinguish mutually different physical channels (user equipment) in each cell from one another.
According to the related art, to obtain a data symbol from a WCDMA signal, after descrambled data are despread with all possible OVSF codes, the used OVSF code is estimated through a maximum likelihood scheme. However, due to the characteristics of OVSF codes in which parent and child branches are not orthogonal with each other, at least two OVSF codes concerned with parent and child branches may be estimated so that the accuracy of the estimation is deteriorated.
(Patent document 1) Related art 1: Korean Unexamined Patent Publication No. 10-2007-0091138 (Title of the invention: Method and apparatus for estimating channelization codes in wireless transmit/receive unit)
(Patent document 2) Related art 2: Korean Unexamined Patent Publication No. 10-2005-0118083 (Title of the invention:)Apparatus and method for allocating OVSF Code AND I/Q channel for reducing peak-to-average power ratio in transmitting data via enhanced up-link dedicated channel in WCDMA system)